1. Field of the Invention
This invention relates to the field of cement compositions and more specifically to the field of cement compositions comprising fluid loss control additives.
2. Background of the Invention
A natural resource such as oil or gas residing in a subterranean formation can be recovered by drilling a well into the formation. The subterranean formation is usually isolated from other formations using a technique known as well cementing. In particular, a wellbore is typically drilled down to the subterranean formation while circulating a drilling fluid through the wellbore. After the drilling is terminated, a string of pipe, e.g., casing, is run in the wellbore. Primary cementing is then usually performed whereby a cement slurry is pumped down through the string of pipe and into the annulus between the string of pipe and the walls of the wellbore to allow the cement slurry to set into an impermeable cement column and thereby seal the annulus. Secondary cementing operations may also be performed after the primary cementing operation. One example of a secondary cementing operation is squeeze cementing whereby a cement slurry is forced under pressure to areas of lost integrity in the annulus to seal off those areas.
The cement compositions typically include a fluid loss control additive to reduce the loss of fluid, e.g., water, from the cement compositions when in contact with permeable subterranean formations and zones. Fluid loss from the cement composition may cause problems such as premature dehydration. Premature dehydration of the cement may lead to problems such as limits on the amount of cement composition that can be pumped; a decrease in the compressive strength of the cement composition; and a negative impact bond strength between the set cement composition and a subterranean zone, the walls of pipe and/or the walls of the wellbore.
Large, water-soluble polymers such as copolymers of acrylamide and 2-acrylamido, 2-methyl propane sulfonic acid have typically been used as synthetic fluid loss control additives. However, such fluid loss control additives may lead to problems such as being useful in a limited number of operations. For instance, the copolymers may not be efficient at higher wellbore circulating temperatures. Moreover, the copolymers may affect the rheology of the cement composition as they may exhibit high viscosity and poor mixability, which may lead to the need of a sufficiently large amount of fluid loss control additive to create a cement composition having an acceptable fluid loss. Such a sufficiently large amount of fluid loss control additive may lead to viscosity and pumpability problems. In addition, some copolymers may not have a salt tolerance suitable for applications involving cement compositions comprising salts. Further drawbacks include that synthetic polymers may not comply with environmental regulations in certain regions of the world. For example, the use of polyamide polymers in the North Sea may be problematic because of the high molecular weight and poor biodegradability of such synthetic polymers.
Consequently, there is a need for a fluid loss control additive that that is suitable for use in a wider range of wellbore circulating conditions. In addition, needs include a fluid loss control additive that is more compliant with environmental regulations. Additional needs include a biodegradable fluid loss control additive. Further needs include a more efficient cement composition comprising a fluid loss control additive.